The song (Gita) of the Lord (Bhagavan).
The Bhagavad Gita is to be found in the 6th book of the Mahabharata. Arjuna refuses to fight and Krishna then conducts this famous doctrinal talk with him.
The Gita was added later. The Mahabharata of Sarala Das is without the Gita.
Read how Arjuna acted without the teaching of Krishna here